310 



ME. HOWARD EOX ON THE 



N. 



gives the general outline of the rock and dykes as seen from the 

 east at extreme low water, and fig. 2 as seen from the west. The 



Fig. 2. — ^^ Man-of-War " EocJcs, as seen from the west. 





^ ^^^^ h 





h, c. Basic dykes. 



cleft A is the best place on which to land. A basic porphyritic 

 dyke, from four to five feet wide, is seen to cut the high rock on the 

 left hand. This dyke can be traced round the back of the rock 

 (6, fig. 2), and appears again after a great fault on the south near 

 the water's edge (c, fig. 2). It has a S.S.E. dip of about 50°. On 

 the north and western side it is thickly studded with crystals of 

 felspar which occasionally weather outside the ground-mass. On the 

 right hand of the cleft A (fig. 1) stands the " Spire " {a, fig. 1). 

 A basic porphyritic dyke, originally several feet thick, cuts the 

 southern end of this rock. At the top of the " Spire " the strike of 

 the gneiss and dyke appear to be conformable, viz., about jS'.N.W. 

 and S.S.E. Below this the dj^ke cuts the gneiss. The dyke 

 weathers out in huge blocks near the top, and in other places forks 

 and branches into veins thinning away to mere threads. Yeins of 

 gneiss occasionally appear to traverse the dyke (see fig. 3), whilst 

 both the gneiss and the dyke are in some places much weathered 

 and altered. Quartz-veins run through both the gneiss and the dykes 

 at right angles. Patches of the dyke are seen adhering to the 

 gneiss on the western summit of this rock, the remainder of the 

 dyke having in that spot jointed out. The gneiss composing the 

 " Man-of-War " rocks is mostly coarse. After repeated and careful 

 observations I believe both strike and dip to be conformable with 

 the Lizard Head schists. "When the " jVIan-of-War " rocks are 

 viewed from the east or west the strike appears to be about east and 

 west, and this is especially the case with the low ledges to the north 

 of the " Spire." When, however, they are viewed from the south in 

 a line with the Lizard Head the conformability of the two is seen 

 pretty clearly. 



The three rocks marked on the 25-inch Parish Map as the " Stags " 

 are composed of coarse gneiss. 



An isolated rock, immediately south of the " Quadrant," is 

 locally known as " Sanspareil." It is composed of somewhat coarse 

 gneiss with a basic porphyritic dyke running about N.W. and S.E. 



